Cationic Engineering Strategy to Achieve Controllable Room-Temperature-Phosphorescence in Hybrid Zinc Halides

Despite rapid progress and wide applications of room temperature phosphorescence (RTP) materials, it is still a great challenge to optimize the RTP activity through rational structural design at a molecular level. Herein, a successful cationic engineering strategy is demonstrated to modulate the crystal flexibility achieving controllable RTP in a new pair of metal halides [APML]ZnCl4 ([APML] = N-(3-Aminopropyl)morpholine) and [AEML]ZnCl4 ([AEML] = N-(2-Aminoethyl)morpholine). Both halides display blue fluorescence under 365 nm UV. Comparing with longer [APML]+, shorter [AEML]+ significantly enhances crystal rigidity and restrains non-radiative scattering, boosting photoluminescence quantum yield (PLQY) from 18.89% to 22.41%. Synchronously, enhanced crystal rigidity significantly promotes the inter-system crossing from singlet to triplet excited states. As a consequence, [AEML]ZnCl4 displays long-lived green RTP property with millisecond scale lifetime in contrast to the blank RTP activity of [APML]ZnCl4. Comprehensive investigations demonstrate that the energy transfer between inorganic and organic components greatly changes the redistribution of singlet and triplet excited states, resulting in distinct phosphorescence activity. The different short-lived blue fluorescence and long-lived green phosphorescence provide a color-time-dual-resolved luminescent tag with advanced applications in anti-counterfeiting, etc. This work highlights a new structural engineering strategy to achieve controllable RTP affording a guide to rationally design RTP materials. A successful cationic engineering strategy is demonstrated to achieve controllable room-temperature phosphorescence in a new pair of metal halides [APML]ZnCl4 and [AEML]ZnCl4. Comparing with the single blue fluorescence of [APML]ZnCl4, the enhanced crystal rigidity of [AEML]ZnCl4 significantly promotes the inter-system crossing from singlet to triplet excitons, which results in dual blue fluorescence and green afterglow with higher quantum yield. The different blue fluorescence and green afterglow provide a color-time-dual-resolved luminescent tag with advanced applications in anti-counterfeiting, etc. image